My girlfriend and I have a fantasy about me tying her to a corner by a leash near my vicinity so she can tend to my "needs" when I call her. The problem is I don't know how to go about setting it up. Is there a special leash or post that I can get that I can easily set up in my apartment and hide easily when we're done? I could just tie the leash around a piece of furniture but that wouldn't really be very secure or realistic for that matter because she could get away lol. Does anyone have any suggestion about how to do this?

You can get one of those retractable leashes with the clickies on the handle and passing the line through the hole in the plastic leash holder, attach it to a leg of the couch or some post near you.
OR
You could attack a hook to the ceiling and tie the leash to that, when people are over just hang a potted plant from it. Just make sure you aren't suspending her or anything. And again, for this type of stuff, retractable leash or a long leash, maybe try to disable the retracting part.

Well one option would be to install a ring in the wall or floor to which you could anchor a chain. That's probably not real likely, given that you're in an apartment, and your landlord might not like it. But you could try installing a ring in a piece of furniture, such as a couch, bed or desk. Mount it on the underside of the furniture where guests won't really notice it. Then padlock a chain to it and lock the other end to a collar your girlfriend wears. Make sure it's a long chain, and light enough that she can move without lots of clanking (unless you want your neighbors to know something odd is going on). Another option would be to chain her to a radiator or some other fixture that has a loop (like the pipes under the kitchen or bathroom sink).

If you are going to leave her chained for long periods when you are away, you need to leave the key where she can get access to it in case she needs to get out. There are two reasons for this. 1) If an emergency arises (such as a building fire), she needs to be able to get out for simple safety reasons. 2) If someone like a landlord or a maintenance person enters the apartment, she needs to not be chained there, unless you want a very unpleasant visit from the police (keep in mind that keeping a woman chained up looks _extremely_ illegal, and in a very bad situation, it might lead to legal charges. 3) If she has a medical emergency, she needs to be able to get to a hospital. I realize that leaving a key where she can access it reduces the power of the fantasy, but bondage play always has to start with safety concerns. If you put someone into bondage, you must always either A) be present to care for them and release them if something goes wrong, or B) ensure that they can get out of the bondage if an emergency arises.

"We hurt the ones we love the most. It's a subtle form of compliment."

Those are all good ideas, and yeah I already considered the safety issues. I don't intend to leave her there, the fantasy is just intended to be part of the light bondage we'll be doing, and I will be near her at all times while she's chained up. We aren't into anything too hardcore, flogging and breast bondage and maybe some blood play would be the extent of what we'll do and we already made the necessary precautions for all of those things so we won't put ourselves in immediate danger.